1. Field of the Invention
The present invention relates to a device for evaluating the reliability of interconnect wires for use in semiconductor devices and, more particularly, to a reliability evaluation technique suitable for lifetime evaluation of interconnect wires due to electromigration (referred to hereinafter as EM) failures.
2. Description of the Background Art
Conventionally, an evaluation TEG (test element group) is widely used for evaluating the reliability of holes such as contact holes and via holes used for interconnection of semiconductor devices. The TEG is constructed such that a hole chain, a pad, and an extension interconnect wire for connecting the pad and the hole chain are formed on an Si substrate.
The conventional evaluation TEG, however, has a situation in which it is difficult to say that the structures of the hole chain and extension interconnect wire are sufficiently optimized for a failure mode. This creates voids resulting from the EM in portions which are not to be evaluated such as a portion of the extension interconnect wire and a portion adjacent a hole connected to the extension interconnect wire portion, not in a portion of the hole chain which is desired to be evaluated, resulting in interconnect wire failure. For example, a hole-to-hole spacing of the hole chain which is as short as several micrometers might result in creation of voids in a portion of the extension interconnect wire provided for establishing a connection between one end of the hole chain and the pad, not in a portion of the hole chain, and accordingly the occurrence of the EM failure.
The voids in the portion which is not to be evaluated cause the EM lifetime of the hole chain to be overestimated or underestimated. It is hence necessary to prevent the creation of such voids.
The predicted value of the EM failure lifetime varies in some cases depending on the establishment of the structure of the hole chain itself. This causes difficulty in stable prediction of the EM lifetime.
Due to these various factors, the reliability evaluation in an EM failure mode using the conventional evaluation TEG fails to exactly predict the EM lifetime.
The above described problems are considered to result from the fact that the structure of the interconnect wires has not been optimized for the evaluation in the EM failure mode. Thus, similar problems are considered to arise in evaluation in other failure modes when a test structure is not optimized in relation to the modes.